Broadband dielectric lens antenna fed by multiconductor quasi-tem lines

ABSTRACT

The apparatus of the present invention provides a feed system utilizing a dielectric lens that is conical on one side and a truncated ellipsoid on the other, with the vertex of the cone coinciding with the focal point of the ellipsoid that is farthest from the convex side thereof. No less than two angular or conical conductors emanating from a multiple-port feed network are disposed longitudinally along the conical portion of the dielectric lens to the point of maximum lens diameter, whereat the conductors are connected together. To achieve monopulse capability and dual polarization, a multiconductor TEM line having no less than five conductors with the proper relative phasing therebetween is used to feed the lens. Proper relative phasing between lines is achieved with a broadband hybrid network.

United States Patent [72] Inventors James S. Ajioka Fullerton; RaymondB. Du Hamel, Los Altos Hills, Calif. [21] Appl. No. 843,554 [22] FiledJuly 22, 1969 [45] Patented Apr. 6, 1971 [73] Assignee Hughes AircraftCompany Culver City, Calii.

[54] BROADBAND DIELECTRIC LENS ANTENNA FED BY MULTICONDUCTOR QUASl-TEMLINES 10 Claims, 2 Drawing Figs.

[52] US. Cl. 343/753, 343/783, 343/854, 343/911 [51] lntJl i ..H0lq19/06 [50] FieldoiSarch 343/753, 754, 755, 783, 853, 911, 854

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[56] References Cited UNITED STATES PATENTS 3,389,394 6/1968 Lewis343/753 3,321,763 5/ 1967 Ikrath et al. 343/754 Primary Examiner-EliLieberman Attorneys-James K. Haskell and Robert H. Himes ABSTRACT: Theapparatus of the present invention provides a feed system utilizing adielectric lens that is conical on one side and a truncated ellipsoid onthe other, with the vertex of the cone coinciding with the focal pointof the ellipsoid that is farthest from the convex side thereof. No lessthan two angular or conical conductors emanating from a multiple-portfeed network are disposed longitudinally along the conical portion ofthe dielectric lens to the point of maximum lens diameter, whereat theconductors are connected together. To achieve monopulse capability anddual polarization, a multiconductor TEM line having no less than fiveconductors with the proper relative phasing therebetween is used to feedthe lens. Proper relative phasing between lines is achieved with abroadband hybrid network.

Patented April 6, 1971 2 Sheets-Sheet 2 BROADBAND DIELECTRIC LENSANTENNA FED BY MULTICONDUCTOR QUASl-TEM LINES The invention hereindescribed was made in the course of or under a contract or subcontractthereunder with the Department of the Army.

BACKGROUND OF THE INVENTION Conventional feeds consist of a relativelysmall antenna such as, for example, a dipole, slot, log-spiral, orlog-periodic antenna which illuminates a reflector or lens with anonuniforrn spherical wave. The reflector converts the radiatedspherical wave into a plane wave for maximum gain or possibly into adifferent spherical wave if a hyperboloidal reflector is used. in thecase of antenna designed on the fourarm equiangular spiral concept,radiation is inherently circu larly polarized, which eliminates some ofthe components from the excitation and polarization assembly. However,to obtain both senses of circular polarization, feeding the spiral fromthe outer end as well as feeding from the center of the spiral has beentried, but with poor performance, because when fed from the outside,higher order radiating modes are encountered by the wave as it travelsin toward the center before it reaches the active radius of the desiredmode. Also, contrawound (clockwise and counterclockwise) spiralsphysically interfere with each other and cannot be used for dualpolarization.

In another concept, a conical array of eight linearly polarizedlog-periodic elements provides sum and dilference patterns for bothsenses of circular polarization simultaneously. Because the relativephase between sum and difference beams is independent of frequency,tracking infonnation is easily obtained. It is difficult, however, toachieve satisfactory impedance or pattern characteristics of thelog-periodic parasitic monopole elements. In addition, the phase centermovement with frequency of even a successful log-periodic antenna usedas a feed for a reflector or lens allows perfect focusing at only onefrequency. The conical transmission line feed system of the presentinvention is simpler, less expensive, and has no phase center movementwith frequency.

SUMMARY OF THE INVENTION The apparatus of the present invention providesan antenna system of more than a decade bandwidth with high directivity,monopulse capability and polarization agility. The system employs aconical or angular transmission line to guide a transverseelectromagnetic (TEM) spherical wave through a dielectric lens whichtransforms the spherical wave into a wave with a planar phase frontwhich radiates into space. Because a TEM wave has no cutoff frequencyand the impedance, phase center location, and aperture fielddistribution are virtually frequency independent, the antenna system isfrequency independent. The beamwidth, however, is limited by theaperture size of the lens in wavelengths. Monopulse operation withdiverse circular polarization is achieved by using equally spacedmulticonductor TEM lines with the proper interelement phase delaysprovided by a broadband hybrid feeding network. The monopulse sum modeutilizes the lowest even radiation pattern mode which requires theinterelement phase between adjacent conical line elements to be 2-rr/nradians where n is the number of conical line elements and for themonopulse difference mode, the lowest odd radiation pattern mode isutilized in which the interelement phase is twice that of the sum mode.A two-conductor feed may be used to obtain a linearly polarized sumpattern. A three-conductor feed can provide two sum beams with oppositecircular polarizations. A four-conductor feed can provide two circularlypolarized sum beams and a degraded difference pattern. Five or moreconductors are required for two circularly polarized sum and differencebeams (four beams in all). In principle, for monopulse operation It mustbe at least three for single circular polarization and at least five fordual circular polarization. However, n is usually chosen for practicalreasons convenient'for the particular broadband hybrid feed ing networkused. Values of six and eight have been used successfully.

For highly directive constant beamwidth antennas, this lens is used as afeed for a reflector (or another lens). The reason for the constantbeamwidth is due to the fact that the lens pattern beamwidth variesinversely with the frequency resulting in a reflector apertureillumination that is constant in terms of wavelengths, thereby insuringa constant beamwidth with frequency change.

In addition to monopulse sum and difference patterns, multipleoverlapping beams (which can be used separately or as amplitudemonopulse schemes) can be obtained by combining the sum and differencemodes M1 M2 where M1 is mode 1 with phase progression Zrr/m a a.

BRIEF DESCRIPTlON OF THE DRAWINGS FIG. 1 illustrates a side view inperspective of the antenna system of the present invention with sixangular conductors; and

FIG. 2 illustrates a block diagram of the sixport feed network of FIG.1.

Referring now to H6. 1 to the drawings, there is shown a side view inperspective of the antenna system of the present invention. Inparticular, the antenna system includes a dielectric lens 10constituting an ellipsoid that is truncated normal to the major axisthereof and a conical section 12 extending from the truncated surface tothe left focal point 13 of the ellipsoid ll, as viewed in the drawing.The dielectric constant of the lens 10 is greater than unity.

In addition to the above, a circular conductor 15 is disposed about thetruncated plane of ellipsoid 11. A conductive sheet 16 is connected tothe conductor 15 and extends outwards therefrom normal to the major axisof the ellipsoid 11. A spacer disc 18 having an aperture in the centerportion thereof and six uniformly spaced holes thereabout is placed overthe vertex of the conical section 12 normal to the axis of rotationthereof. The aperture of the disc 18 is of the order of 1 inch indiameter to allow the vertex of conical section 12 to extend acomparable distance therethrough. Six flat conductors are disposed fromthe spaced holes in disc 18 to the circular conductor 15. The flatconductors 20-25 taper outwards to approximately midlength and thentaper in for the remainder of the length. Optimum configuration of theflat conductors 20- --25 varies with the frequency. The six flatconductors 20- 25 about lens 10 are connected to a six-conductor TEMline 27 whereby the six conductors thereof constitute inputs to theantenna system and are designated T,T respectively. The terminals T,-Tconnect to a six-port feed network 28 which has 2 (summation) inputs 30,31 and A (difference) inputs 32, 33. The summation inputs 30, 31 feedthe flat conductors 20- 25 about the lens 10 with progressivelyincreasing or decreasing phase of 60 to produce single beams of rightcircular and left circular polarization. The difference inputs 32, 33,on the other hand, feed the flat conductors 20-25 about the lens 10 withprogressively increasing or decreasing phase of which accumulates to 720in one revolution to generate dual beams of right circular and leftcircular polarization for tracking purposes. The right and left circularpolarized beams may be operated simultaneously to generate a linearpolarized beam that is poled in any desired direction.

Referring to H6. 2, there is shown a schematic block diagram of thesix-port feed network 28 of FIG. 1. The six-port feed network 28constitutes an emperical combination of quadrature hybrid andtapered-line magic-T networks. In FIG.

2 a convention is used in connection with the respective quadraturehybrids wherein the feed side comes out in phase quadrature with thenonfeed side and the label H refers to a 3 db. quadrature hybrid whereinthe input power is divided equally between the two output terminals. lnaddition, a convention is used in-connection with tapered line magic-T'swherein one side is defined as the 2" side. The label T refers to a 3db. tapered-line magic-T for which the coupled outputs are split inpower by the ratio lzl and the label T refers to a 4.8 db. tapered-linemagic-T for which the coupled outputs are split in power by the ratio of2:1 with the greater power output being on the 2 side. When feed isapplied to the Z-side, the voltages appearing at the outputs are inphase and when the feed is applied to the non-2 side the voltagesappearing at the outputs are l80 out of phase.

Referring now to FIG. 2, the six-port feed network 28 includes terminals34-39 which connect, respectively, to terminals T,T and include 3 db.tapered-line magic-T's 40, 41, which have E-side outputs connected toterminals 35, 38 and the non-2 side outputs connected to terminals 36,39, respectively. In addition, network 28 includes 4.8 db. tapered-linemagic-T's 42, 43 which have i-side outputs connected to terminals 34,37, respectively, non-2 side outputs connected to the Z-side inputs oftapered-line magic-Ts 41, 40, respectively, and the E-side inputsterminated with impedances 44, 45 respectively. An additional 3 db.quadrature hybrid 46 has an output 47 connected to the non-2 side inputof 4.8 db. tapered-line tapered-line magic-T 41. Quadrature hybrid 46has inputs 49, 50 opposite outputs 47, 48, respectively. Similarly, anadditional 3 db. quadrature hybrid 51 has an output 52 connected to thenon-2 side input of tapered-line magic-T 40 and an output 53 connectedto the non-)1 side input of tapered-line magic-T 43. Quadrature hybrid51 has inputs 54, 55 opposite the outputs 52, 53, respectively. Lastly,3 db. tapered-line magic-Ts 60, 61 have E-side outputs connected toinputs 50, 55, and non-2 side outputs connected to inputs 54, 49,respectively, of quadrature hybrids 46 and 51. The E-side inputs oftapered-line magic-T's 60, 61 are connected to A-tenninals 32, 33,respectively, and the non-Eside inputs to Z-terrninals 31, 30,respectively.

In operation, a signal applied to E-tenninal 30 corresponds to a sumpattern excitation and produces progressive phases at the terminals T--T of 60. A signal applied to Z-tenninal 31, on the other hand,produces a sum pattern of the opposite circular polarization of phaseprogression of 60 at the terminals T -T Likewise, a signal applied toA-terminals 32 or 33 produces difference patterns with phaseprogressions of H20 or l20, respectively, at the terminals T,T Theenergy available at the terminals 34-39 progresses through the TEM line27 to the flat conductors 20-25 which form a conical transmission line.The constant phase surfaces for the electric and magnetic fields arespheres centered at the focal point 13. Since the phase fronts for thetransmission line wave are spherical, the lens will tend to transmitthis wave as a plane wave. Sum patterns produce a single main beam anddifference patterns produce two overlapping beams suitable for trackingpurposes.

We claim:

1. A broadband antenna system comprising an ellipsoid of dielectricmaterial of predetermined dielectric constant, truncated nonnal to themajor axis thereof between one focal point and the extremity of saidmajor axis farthest therefrom and a cone of dielectric material of saidpredetermined dielectric constant extending from the truncated surfaceof said el lipsoid to said one focal point, thereby to provide adielectric lens;

a circular conductor disposed about the periphery of said truncatedsurface of said ellipsoid;

a plurality of no less than two equal length flat conductors disposedlongitudinally along and at uniform intervals about said cone commencingfrom said circular conductor; and

a transmission line having a corresponding plurality of conductorsconnected to the respective extremities of said plurality of flatconductors farthest'from said circular conductor.

2. The broadband antenna system as defined in claim 1 wherein saidpredetermined dielectric constant is greater than unit 3 A broadbandantenna system comprising an ellipsoid of dielectric material ofpredetermined dielectric constant truncated normal to the major axisthereof between one focal point and the extremity of said major axisfarthest therefrom and a cone of said dielectric material extending fromthe truncated surface of said ellipsoid to said one focal point therebyto provide a dielectric lens;

a circular conductor disposed about the periphery of said truncatedsurface of said ellipsoid; and

means disposed on said cone of said dielectric lens for providing an nconductor conical transmission line from the vertex thereof to saidcircular conductor, n being an integer no less than two.

4. The broadband antenna system as defined in claim 3 wherein said nconductor conical transmission line includes n flat conductors having ataper from the center portion thereof.

5. The broadband antenna system as defined in claim 3 additionallyincluding a conductive sheet extending outwards from said circularconductor.

6. A broadband antenna system comprising an ellipsoid of dielectricmaterial of predetennined dielectric constant truncated normal to themajor axis thereof between one focal point and the extremity of saidmajor axis farthest therefrom and a cone of said dielectric materialextending from the truncated surface of said ellipsoid to said one focalpoint thereby to provide a dielectriclens',

a circular conductor disposed about the periphery of said truncatedsurface of said ellipsoid; n equal length flat conductors disposedlongitudinally along and at uniform intervals about said cone commencingfrom said circular conductor where n is an integer no less than two;

a TEM transmission line having n conductors connected to respectiveextremities of said n flat conductors farthest from said circularconductor; and

means connected to said TEM transmission line for feeding said n fiatconductors with signals having substantially equal phase differencesfrom one conductor to the next adjacent conductor.

7. The broadband antenna system as defined in claim 6 wherein n is aninteger no less than three and said substantially equal phasedifferences from one conductor to the next adjacent conductorconstitutes a phase progression of 360/n.

8. The broadband antenna system as defined in claim 6 wherein n is aninteger no less than three and said substantially equal phasedifferences from one conductor to the next adjacent conductorconstitutes a phase delay of 360ln.

9. The broadband antenna system as defined in claim 6 wherein n is aninteger no less than five and said substantially equal phase differencesfrom one conductor to the next adjacent conductor constitutes a phaseprogression of 720n.

10. The broadband antenna system as defined in claim 6 wherein n is aninteger no less than five and said substantially equal phase differencesfrom one conductor to the next adjacent conductor constitutes a phasedelay of 720/n.

1. A broadband antenna system comprising an ellipsoid of dielectricmaterial of predetermined dielectric constant, truncated normal to themajor axis thereof between one focal point and the extremity of saidmajor axis farthest therefrom and a cone of dielectric material of saidpredetermined dielectric constant extending from the truncated surfaceof said ellipsoid to said one focal point, thereby to provide adielectric lens; a circular conductor disposed about the periphery ofsaid truncated surface of said ellipsoid; a plurality of no less thantwo equal length flat conductors disposed longitudinally along and atuniform intervals about said cone commencing from said circularconductor; and a transmission line having a corresponding plurality ofconductors connected to the respective extremities of said plurality offlat conductors farthest from said circular conductor.
 2. The broadbandantenna system as defined in claim 1 wherein said predetermineddielectric constant is greater than unity.
 3. A broadband antenna systemcomprising an ellipsoid of dielectric material of predetermineddielectric constant truncated normal to the major axis thereof betweenone focal point and the extremity of said major axis farthest therefromand a cone of said dielectric material extending from the truncatedsurface of said ellipsoid to said one focal point thereby to provide adielectric lens; a circular conductor disposed about the periphery ofsaid truncated surface of said ellipsoid; and means disposed on saidcone of said dielectric lens for providing an n conductor conicaltransmission line from the vertex thereof to said circular conductor, nbeing an integer no less than two.
 4. The broadband antenna system asdefined in claim 3 wherein said n conductor conical transmission lineincludes n flat conductors having a taper from the center portionthereof.
 5. The broadband antenna system as defined in claim 3additionally including a conductive sheet extending outwards from saidcircular conductor.
 6. A broadband antenna system comprising anellipsoid of dielectric material of predetermined dielectric constanttruncated normal to the major axis thereof between one focal point andthe extremity of said major axis farthest therefrom and a cone of saiddielectric material extending from the truncated surface of saidellipsoid to said one focal point thereby to provide a dielectric lens;a circular conductor disposed about the periphery of said truncatedsurface of said ellipsoid; n equal length flat conductors disposedlongitudinally along and at uniform intervals about said cone commencingfrom said circular conductor where n is an integer no less than two; aTEM transmission line having n conductors connected to respectiveextremities of said n flat conductors farthest from said circularconductor; and means connected to said TEM transmission line for feedingsaid n flat conductors with signals having substantially equal phasedifferences from one conductor to the next adjacent conductor.
 7. Thebroadband antenna system as defined in claim 6 wherein n is an integerno less than three and saId substantially equal phase differences fromone conductor to the next adjacent conductor constitutes a phaseprogression of 360*/n.
 8. The broadband antenna system as defined inclaim 6 wherein n is an integer no less than three and saidsubstantially equal phase differences from one conductor to the nextadjacent conductor constitutes a phase delay of 360*/n.
 9. The broadbandantenna system as defined in claim 6 wherein n is an integer no lessthan five and said substantially equal phase differences from oneconductor to the next adjacent conductor constitutes a phase progressionof 720*n.
 10. The broadband antenna system as defined in claim 6 whereinn is an integer no less than five and said substantially equal phasedifferences from one conductor to the next adjacent conductorconstitutes a phase delay of 720*/n.